A mother-of-three braved death to push her children to safety moments before a car ran her down at the gates to Downing Street.

Witnesses described how the woman, on holiday with her family from America, was flung five metres as the red Vauxhall Astra smashed into the reinforced gates barring access to the Prime Minister's residence at 1231GMT.

Police rushed to her aid as colleagues pounced on the blond-haired driver of the T-registration car, pulling him to the ground and handcuffing him, as Whitehall's most sensitive address was flooded with protection officers.

The woman, who is in a comfortable condition in hospital with a broken leg, was emerging through the gates with her family after being allowed to walk up to the famous Number 10 door when the collision happened.

Pushed to safety

Her three sons - aged three, six and eight - escaped the ordeal virtually unscathed as their mother, who was accompanied by her husband, sacrificed her own safety in the face of the careering car.

Eye witness Sertac Bahri, who was taking part in a protest outside the gates said: "We heard the car skidding in and jumped out to look.

"I saw the woman push her children out of the way to save them from getting hit, but the car went into the woman instead.

"She flew up in the air legs first and landed about five metres away. The police rushed in from all directions and opened the car door and pulled out the man who they pushed to the floor and handcuffed."

The driver, described as 30-35 with spiky hair, is being held at nearby Charing Cross police station ahead of questioning by CID officers on suspicion of causing criminal damage.

Scotland Yard said terrorism was not behind the incident, but added that inquiries were continuing to find out whether the man had driven deliberately at the formidable steel barrier, or simply lost control of the vehicle.

PM's concern

Downing Street confirmed that the Prime Minister and his family were not in their home at Number 11 at the time of the incident - and said Mr Blair would be writing personally to the brave mother, who has not been named.

A spokeswoman said: "The Prime Minister and Mrs Blair were not in Downing Street at the time. The Prime Minister has asked to be kept informed of the lady's progress and he will be writing personally to her."

St Thomas's Hospital, where the woman and her family were receiving treatment, said the three children were being treated for minor injuries while the mother was to be admitted ahead of possible surgery.

Dr David Williams, accident and emergency consultant, said: "The father had no injuries and the three children are being assessed for minor injuries before being likely to be discharged.

"The mother has a broken leg and will be admitted to hospital for treatment by an orthopaedic surgeon."

He added that no further personal details of the family would be released at their request.

Senior officers are expected to examine damage to the gates on Monday after a support strut was broken in the crash and the bolt connecting the gates to the ground was bent.

A spokeswoman said: "There was no danger to the security of Downing Street. The injured woman received rapid treatment while the driver was quickly detained.

Police probe

He remains in custody and will be further questioned by officers."

It is not thought that the 28-year-old driver, who has not been identified, was known to the victims.

Eye witnesses described how his car had been travelling up Whitehall towards Trafalgar Square and stopped in front of a bus before suddenly performing a dramatic U-turn and driving into Downing Street.

Skid marks from the 16 valve car, which was quickly removed from the scene with damage to the front right side, were also clearly visible.

Peter Saacs, 55, who was driving the Stagecoach bus, said: "The driver (of the car) pulled up as if to show someone Downing Street.

"Then he was wheel-spinning in front of me and pulled out and went round the back of our bus and into the gates."

The ornate black and gold gates were erected in 1989 on the orders of then prime minister Margaret Thatcher, amid strong opposition at the time from Labour.

Former prime minister John Major and his Cabinet narrowly escaped injury two years later when an IRA gang fired three mortar bombs from a Ford Transit van in a nearby street.

One of the weapons landed in the garden behind Number 10, blowing out windows in nearby buildings.